MB Sprinter Charging House Batteries

[mlmay12]

The strangest thing happened on my last trip. I have a Victron BMV-712 Smart Battery Monitor. I use my phone with the Victron bluetooth app and am very diligent about keeping an eye on whats happening with my batteries. On the long drive home I noticed the Alternator was providing no charge to my house batteries. Being at 70% SOC, I thought I would run my Generator for a while to charge them. I couldn't remember if in the past my Alternator provided any charge while driving to the house batteries. My Converter is a PD4060LICSV and puts out 60A.

After my generator came online I noticed my batteries were receiving about 90A. I immediately shut off the generator after about only 30 seconds and observed that my alternator was now providing about 45A to the house batteries. I let it continue while watching it and in about an hour of driving they were at 100% SOC and the alternator current to them dropped to 0A. I tried this again the next day with the same result.

Not having any wiring diagrams from Dynamax, I can only figure that starting the generator establishes a connection from the house batteries to the chassis battery to provide a charge from the converter, but also allows the alternator a connection to the house batteries.

Very strange, anyone have any ideas?

[rk06382]

Originally Posted by mlmay12

The strangest thing happened on my last trip. I have a Victron BMV-712 Smart Battery Monitor. I use my phone with the Victron bluetooth app and am very diligent about keeping an eye on whats happening with my batteries. On the long drive home I noticed the Alternator was providing no charge to my house batteries. Being at 70% SOC, I thought I would run my Generator for a while to charge them. I couldn't remember if in the past my Alternator provided any charge while driving to the house batteries. My Converter is a PD4060LICSV and puts out 60A.

After my generator came online I noticed my batteries were receiving about 90A. I immediately shut off the generator after about only 30 seconds and observed that my alternator was now providing about 45A to the house batteries. I let it continue while watching it and in about an hour of driving they were at 100% SOC and the alternator current to them dropped to 0A. I tried this again the next day with the same result.

Not having any wiring diagrams from Dynamax, I can only figure that starting the generator establishes a connection from the house batteries to the chassis battery to provide a charge from the converter, but also allows the alternator a connection to the house batteries.

Very strange, anyone have any ideas?

Do you have a Precision Circuits Inc. LiFePO4 Battery Isolation Manager 225? It has a duty cycle of 15 minutes on every 35 minutes. see below. It could explain the weird behavior you described above.

From I found this on Battle Born's website.

Precision Circuits Inc. LiFePO4 Battery Isolation Manager 225

Under normal charging conditions, the BIM will connect for 15 minutes every 35 minutes. That means that the BIM will connect for 15 minutes, disconnect for 20 minutes, and repeat this cycle until the coach battery is charged.
If the coach battery resting voltage exceeds 13.4V than the BIM will disconnect. A resting voltage greater than 13.4V indicates a fully charged battery. Note that “resting voltage” means that no current is flowing to the coach battery.
The BIM will disconnect if the alternator voltage exceeds 14.4V. This protects the coach battery from overcharging.
The BIM will disconnect if the voltage difference between the alternator and the coach battery is less than 0.1V. If the voltage difference is too low, then there is a negligible charging current, and no need to connect to the coach battery
The BIM will disconnect if the alternator voltage drops below 13.3V. If the alternator voltage is too low, than it cannot adequately charge the coach battery, so there is no reason to connect. Made in the USA.

Another thread: Forester Transit - Charging of Lithium House Batt

[mlmay12]

Originally Posted by rk06382

Do you have a Precision Circuits Inc. LiFePO4 Battery Isolation Manager 225? It has a duty cycle of 15 minutes on every 35 minutes. see below. It could explain the weird behavior you described above.
Attachment 194648
From I found this on Battle Born's website.

Precision Circuits Inc. LiFePO4 Battery Isolation Manager 225

Under normal charging conditions, the BIM will connect for 15 minutes every 35 minutes. That means that the BIM will connect for 15 minutes, disconnect for 20 minutes, and repeat this cycle until the coach battery is charged.
If the coach battery resting voltage exceeds 13.4V than the BIM will disconnect. A resting voltage greater than 13.4V indicates a fully charged battery. Note that “resting voltage” means that no current is flowing to the coach battery.
The BIM will disconnect if the alternator voltage exceeds 14.4V. This protects the coach battery from overcharging.
The BIM will disconnect if the voltage difference between the alternator and the coach battery is less than 0.1V. If the voltage difference is too low, then there is a negligible charging current, and no need to connect to the coach battery
The BIM will disconnect if the alternator voltage drops below 13.3V. If the alternator voltage is too low, than it cannot adequately charge the coach battery, so there is no reason to connect. Made in the USA.

Another thread: Forester Transit - Charging of Lithium House Batt

Thanks for replying, I currently have the stock Precision Circuits BIM installed by Dynamax. I thought this would work fine because it shut the charging current down from the converter to the chassis/starting battery when it reached 13.6V allowing the house batteries to continue charging until 100% without overcharging the chassis/starting battery. I just assumed the chassis/starting battery was being charged or not charged as it normally is by the alternator. I was wondering why the House Batteries were suddenly being charged by the alternator, not that I would complain about that. I will look into this BIM but heard there can be an installation issue as it doesn't fit into the same place as the stock BIM.